1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display having a thin film transistor and a pixel electrode.
2. Discussion of the Related Art
Generally, a thin film transistor-liquid crystal display (TFT-LCD) includes a bottom plate on which a thin film transistor and a pixel electrode are arranged and a top plate on which a color filter for displaying colors and a common electrode are formed. Liquid crystal is filled between the bottom and top plates.
FIG. 1 is a layout of a thin film transistor and a pixel electrode arranged on the bottom plate of a conventional liquid crystal display.
Referring to FIG. 1, a gate line G/L is arranged in the horizontal direction, and a data line D/L is arranged in the vertical direction. A thin film transistor is formed at an intersection where gate line G/L and data line D/L meet. Gate line G/L is used as a gate electrode G of the thin film transistor and data line D/L as its source electrode S. A pixel electrode P is coupled to a drain electrode D of the thin film transistor.
A conventional structure of a thin film transistor and a pixel electrode of a liquid crystal display and a method of fabricating the same will be discussed below with reference to the accompanying drawings.
FIGS. 2A-2F are cross-sectional views of a sequential manufacturing process of the thin film transistor and pixel electrode of the conventional liquid crystal display, taken along line A--A' of FIG. 1.
First, as shown in FIG. 2A, a gate electrode 2 is formed on a glass substrate 1. Then a gate insulating layer 3, amorphous silicon layer 4, n+amorphous silicon layer 5, and Cr layer 6 are sequentially formed on the overall surface of substrate 1 including gate electrode 2.
Next, as shown in FIG. 2B, the active region of the thin film transistor is defined so that amorphous silicon layer 4, n+amorphous silicon layer 5, and Cr layer 6 are selectively removed such that these layers remain only on the active region and over what will become the source and drain regions. A Cr silicide layer 7 is formed between Cr layer 6 and n+amorphous silicon layer 5 by annealing the resultant structure between 150 and 300.degree. C. for 30-60 minutes.
As shown in FIG. 2C, a negative-type photoresist 8 is coated on the overall surface of the substrate including the Cr silicide layer 7, and back-side exposure and development are performed using gate electrode 2 as a mask. Then, as shown in FIG. 2D, photoresist 8 coated on gate electrode 2 is removed selectively to expose a portion of the Cr silicide layer 7.
As shown in FIG. 2E, exposed Cr silicide layer 7 and n+amorphous silicon layer 5 are sequentially removed using the remaining photoresist 8 as a mask. Photoresist 8 is also removed.
Next, as shown in FIG. 2F, a nitride 10 is deposited on the overall surface of the substrate, and a contact hole is formed on Cr silicide layer 7. A source electrode S and drain electrode D are formed to come into contact with Cr silicide layer 7 through the contact hole. A pixel electrode P (not shown) is formed to come into contact with drain electrode D.
However, the conventional liquid crystal display formed by the aforementioned method has the following problems.
First, the substrate is bent due to stress caused by compression during deposition of the metal layer, and the aperture ratio is reduced as much as the region occupied by the metal layer, because the metal layer is formed on the drain electrode (or source electrode) of the thin film transistor, which is coupled to the pixel electrode.
Second, steps or levels are formed because the source/drain electrodes of the thin film transistor are formed of metal and the pixel electrode contacts the source/drain electrodes from above.
Third, metal deposition processes for forming the silicide and source/drain electrodes are performed separately, complicating the overall manufacturing procedure.
Fourth, a drain electrode made of metal is formed in the drain region of the thin film transistor, reducing the aperture ratio.